Process for testing a head stack assembly

ABSTRACT

A new fixture which is capable of holding an HAS throughout all processes so that Quasi-Static Test can be done before swaging. Also, a process for testing the HAS by means of the fixture. An embodiment method may include loading head gimbal assemblies and an actuator using an automatic loading machine; in-line dressing of the head gimbal assemblies; ultrasonic bonding of the head gimbal assemblies; testing said head gimbal assemblies in-line while quasi-static; and if an head gimbal assemblies fails to pass the testing, rejecting and reworking in-line; in-line coating of the head gimbal assemblies; ultra-violet curing of the head gimbal assemblies; in-line swaging said head gimbal assemblies and actuator to form an head stack assemblies; and visual checking and unloading of said head stack assemblies.

RELATED APPLICATION

This application is a Divisional of patent application Ser. No.10/294,977, filed on Nov. 13, 2002, and issued as U.S. Pat. No.6,859,995 B2 on Mar. 1, 2005, which claims the benefit of priority toPCT/CN01/01550, filed on 13 Nov. 2001.

CROSS REFERENCE TO RELATED DOCUMENTS

The present application claims the benefit of CHINA PCT/CN01/01550 filedNov. 13, 2001, which is hereby incorporated by reference herein in itsentirety.

FIELD OF THE INVENTION

The present invention generally relates to a fixture for a hard diskdrive, and specifically, to a universal fixture for a head stackassembly (HSA) in the hard disk driver used in a computer, and to aprocess for testing both wire and wireless types of HSA products in harddisk drive industry by means of the universal fixture.

BACKGROUND OF THE INVENTION

Typically, a disk drive comprises one or more magnetic disks havingmagnetic surfaces for data storage. The disks are mounted on a spindleand continually rotated at a substantially constant speed. A pluralityof head arm assemblies are arranged together in a stacked assemblyresembling a comb-type structure. The main body of the HSA is anelectromagnetic actuator which is controlled by a head positioningsystem. The actuator positions the magnetic heads or transducers topreselected concentric recording tracks under the control of an addresssignal supplied to the actuator from a data processing system.

Each transducer, or head, glides over the disk surface by a film of aircreated by the disk as it is rotated. This type of head as designated bynumeral 101 in FIG. 1 is classified as “an air bearing head” and isattached to a flexible sheet metal member 102 by means of a gimbal typemounting. The pre-formed sheet metal, which is called load beam, is madeof stainless steel and is connected to a nut plate 103 with laser welds.A combination of “load beam”, “gimbal type structure” and “air bearinghead” is called Head Gimbal Assembly (HGA) 1. The HGA 1 is swaged to anactuator 2 comprising a body 201 on which a bearing 204 is mounted, avoice coil 202 arranged between two legs 205 of the body 201 and anumber of arm fingers 203 extending from the body (FIGS. 2A and 2B). Thehead 101 is allowed to be biased toward the magnetic surface of therotating disk for accessing the stored data.

The transducer is supplied with data signals during the recording modeof the disk drive. During reading of the recorded data, the transducersenses the magnetic transitions recorded on the disk representing thedata. Each disk surface is associated with one HGA which, after beingstacked up onto the actuator, forms a comb-type structure having thetransducers at the distal ends of the HGAs with accurate verticalalignment. The complete assembly of HGAs with an actuator is called anHSA 3 (FIG. 2B) which is controlled to move over a corresponding pathinside the hard disk drive.

In addition, the individual components on the HGA become more fragileand are easily damaged if extreme care is not exercised during each ofthe assembly operations. A head arm assembly operation generallycomprises joining together a relatively stiff element and a relativelyflexible element by a swaging operation. A head gimbal assembly (HGA) 1comprises a magnetic transducer and a grimbal type mount attached to thedistal end of the flexible element, usually by spot welding. The otherend of the flexible element has a nut plate welded to the stiff element.The nut plate includes a cylindrical boss which extends normal to theflat surface of the plate and is designed to mate with an openingdisposed in the end section of the rigid element. The elements arealigned precisely and spot welded to maintain their alignment during thesubsequent swaging operation. The swaging operation as shown in FIG. 3involves a series of steps in which a ball 32 slightly larger than theopening in a cylindrical boss 31 (not precisely scaled) is forcedthrough the boss 31 thereby cold forming the boss material to the areaof the rigid element surrounding the boss. This swaging operation hasbecome the most critical step in the manufacturing process as the sizeof the components has decreased and their fragility has increased. Thebiasing force for the magnetic transducer is provided in the flexibleelements by bending the flexible element along a line perpendicular tothe lengthwise axis of the arm and subsequently returning the element toits original position while simultaneously stress relieving the bendarea by heating it with a laser until the desired gram load force isobtained. The required gram load is determined by the flyingcharacteristics of the transducer relative to the magnetic surface.

Assembly operations of the HSA involve providing a guide means, such asa guide hole, in the actuator end of the head arm. Each HGA issequentially placed on a shaft with suitable ring type spacers betweeneach arm. Each arm is affixed to the shaft by ball swaging or adhesive.

The HSA is provided with a shipping comb which functions to maintain theadjacent head arms spaced apart a predetermined distance while the HSAis being tested before installation in the disk drive. The shipping combis arranged to pivot out of position during the gram load measuringoperation to permit each head to apply a force to a sensing device thatmeasures and displays the value of the gram load of that head to theoperator.

After positioning the HSA on a platform, the operator moves the platformto the measurement position. The heads are measured one at a time. Forexample, where the HSA includes four heads, four separate sensingdevices are provided so that the operator is advised if any head is outof specification.

With the decrease in size, the head arms become less sturdy and henceare more sensitive to the swaging operation with the result that thealignment of the heads may be adversely affected. Further, if an HGA armproves, on testing of the head stack, to be out of specification for thegram load, the possibility of manually adjusting the flexible element toobtain the correct biasing force is almost impossible.

The rework operation to replace the HGA having the incorrect gram loadwith a new head, or to at least salvage the good head arms, (usually 3arms) was very complicated due to the swaging construction and the morefragile nature of the smaller components.

A conventional HSA assembly process in which quasi-static testing (QST)can only be done after swaging and the rework process always requiresde-swaging when HGA needs to be removed. This type of rework process isalways time consuming, deforms the actuator, creates tremendous amountof particles and damages other quality HGA as well.

In order to overcome these problems, an HGA out of specification has tobe identified before being swaged tightly to the actuator. It means thatQST has done preferably before swaging so that the HGA out ofspecification can be replaced without going through the de-swagingprocess.

Consequently, a universal fixture is needed to hold HGAs in place whilean HSA is being processed through various assembling and testingoperations.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a universal fixturefor an HSA assembly.

Another object of the present invention is to provide a process fortesting the HSA assembly by means of the universal fixture.

The universal fixture is structured in such a way that it can carry theHSA throughout all processes, including HGA auto-loading, bonding, QSTand swaging. Some parts of the fixture are made of either ceramics ornon-magnetic materials so that the QST of the HSA can be done with thefixture prior to HGAs being swaged tightly to an actuator.

If an HSA fails the test, one HGA out of specification can be replacedimmediately in-line with another HGA of the same type, and an HSA whichpasses the QST can be proceeded to swaging.

Having employed the universal fixture in accordance with the presentinvention, the yield of the HGA can be improved by 10%. A minimum spaceis needed for rework of an HSA failed in the QST, and process loopingtime for the rework cycle is reduced significantly from a half day toonly 2 minutes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater details withreference to the drawings, in which:

FIG. 1 is a perspective view of an HGA;

FIG. 2A is a perspective view of an HGA and an actuator before theirassembling;

FIG. 2B is a perspective view of an HGA and an actuator after theirassembling;

FIG. 3 is a diagram showing a swage operation of an HSA;

FIG. 4 is a perspective view of a universal fixture of the presentinvention with an HGA fitted to a respective arm finger of an actuator;

FIG. 5 is an exploded view of a universal fixture of the presentinvention;

FIG. 6 is a flow-chart of the HSA assembling process in accordance withthe present invention; and

FIG. 7 shows a comparison of the rework process of the present inventionwith that of the prior art.

DETAILED DESCRIPTION

The present invention will be better understood by reading the preferredembodiments of the invention with reference to the drawings.

FIG. 4 is a perspective view of a universal fixture of the presentinvention with an HGA fitted to a respective actuator, and FIG. 5 is anexploded view of the universal fixture of the present invention. Asshown in FIGS. 4 and 5, the universal fixture for an HSA assemblyaccording to the present invention comprises a platform 10 made ofstainless steel, on which provided are an alignment pin holder 11, awedge holder 12, a set of wedge plates 13 made of ceramic ornon-magnetic materials for holding HGA's, an alignment pin 14 foraligning each HGA by passing through an aperture in the load beam of theHGA, an alignment datum pin 15 for limiting rotational stroke of theactuator, a datum pin 16 passing through an bearing opening of anactuator for fixing rotationally the actuator, an AFA clamper 17 forclamping an AFA (arm finger of actuator) and a handle 18 fixed at oneend of the platform 10. The wedge holder 12 is mounted onto the platform10 by means of screws, and is provided with several parallel horizontalslots the number of which correspond to that of the wedge plates 13 sothat these parallel horizontal slots can receive respective wedge plates13 when they are fitted separately and rotationally into the wedgeholder 12 by means of a shaft 19, as shown in FIG. 5. One of the freeends of each wedge plate 13 is of an “F” shaped fork, and of twoparallel arms of the fork, a farther arm of the fork is wider than anearer arm. In the wider arm provided is an opening whose diametercorresponds to that of the swaging opening of the nut plate of the HGA.The end of each of the two arms is partly cut off so that a thin tip isformed on one side at the end of each arm. The alignment pin holder 11is mounted onto the platform 10 by means of a few pins 20, and part ofthe alignment pin holder 11 is cut off so that a rectangular recess 21is formed in the alignment pin holder 11. On one of vertical walls ofthe rectangular recess 21 there are provided with a few webs 22, thenumber of which also correspond to that of the wedge plates 13. At thedistal end of each web 13 formed is an aperture whose inner diameter isslightly larger than the diameter of the alignment pin 14 so that thealignment pin 14 can freely pass through the aperture. The datum pin 16consist of two parts that are sized so that they can extend partly andoppositely into the bearing hole of an actuator.

During the in-line process of HGAs, an actuator is fixed to theuniversal fixture by the datum pin 16, and the opening of each armfinger of the actuator is aligned with that of respective wedge plates13. A plurality of HGAs the number of which corresponds to that of thearm fingers of the actuator are loaded onto the universal fixture bymeans of the wedge plates 13 and the webs 22. The universal fixture ofthe present invention is structured in such a way that it can carry theHSA throughout all processes, including auto-loading, bonding, quasistatic testing and swaging, and the quasi static test of the HSA can bedone with the fixture prior to the HGA being swaged tightly to anactuator.

An in-line process of an HGA by the universal fixture of the presentinvention will be explained with reference to FIG. 6. This in-lineprocess generally comprises following steps:

Auto-loading the machine by loading HGAs and an actuator;

In-line dressing;

Ultrasonic Bonding;

In-line quasi static testing of HGAs;

If an HGA fails to pass the testing, it will be rejected and in-linereworked;

In-line coating;

Ultra-voilet curing;

In-line swaging of the HGAs and actuator to form an HSA; and visualchecking and unloading of the HSA.

In the in-line process of the invention, since the wedge plates 13 ofthe fixture can operated independently each other, if an HSA fails thequasi static test, a failing HGA can be replaced in-line immediately andthe same HSA can be retested again. Only quality HSAs which pass thequasi static test can be proceeded to swaging.

FIG. 7 shows a comparison of the rework process of the present inventionwith that of the prior art. As shown in FIG. 7, the prior normal flowrework process comprises steps: off-line quasi static test of an HSA;rejection of an failing HSA; remove of a bearing; de-swage of the HSA;cleaning of the de-swaged HSA; installation of the bearing; swage of theHSA; bonding of HGAs; and quasi static test of the HSA again.Consequently, the process of the prior art has a lower QST yield afterrework with deformation and contamination of the HSA.

In contrast, the in-line rework process of the present inventioncomprises only steps: in-line quasi static test of an HSA; in-linerework of the failing HSA; bonding HGAs; and quasi static test of theHSA again. Consequently, the process of the present invention has abetter QST yield after rework without deformation and contamination ofthe HSA.

It will be understood that the invention is not restricted to theaforedescribed and illustrated exemplifying embodiments thereof and thatmodifications can be made within the scope of the inventive conceptdefined in the following claims.

1. A method for testing a head stack assembly comprising: loading headgimbal assemblies and an actuator using an automatic loading machine;ultrasonic bonding of said head gimbal assemblies; in-line quasi statictesting of said head gimbal assemblies; in-line coating of said headgimbal assemblies; ultra-violet curing of head gimbal assemblies;following said in-line quasi-static testing, in-line swaging said headgimbal assemblies and actuator to form head stack assemblies; visualchecking and unloading of said head stack assemblies; and wherein if ahead gimbal assemblies fails to pass the testing, rejecting andreworking the head gimbal assemblies in-line.
 2. A process for testinghead stack assemblies according to claim 1, wherein ultrasonic bondingand in-line quasi static testing follow in-line rework.